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GATE Previous Years Solved Papers: EE MADE ERS
4.26 A stand alone engine driven Synchronous The rotor mmt lags stator mmf by a space and
generator is feeding a partly inductive load. A at any instant as shown in figure. Thus, har
capacitor is now connected across the load to stator and rotor surfaces will form one pole
completely nullify the inductive current. For this the other half forming the second pole For
operating condition,
the direction of torque acting on the rotor cany
(a) the field current and fuel input have to be
clockwise or counter-clockwise.
reduced
(b) the field current & fuel input have to be
Airgap
increased
-Rotor
(c) the field current has to be increased & fuel
F.
input left unaltered
son the field current has to be reduced & fuel input
left unaltered
Rotor mmf axis
[2003 : 1 Mark)
Ca
Stator
co
16
*
- Staforma
OA
4.27 Curves X and Yin figure denote open circuit and
full-load zero power factor (zpt) characteristics of
a synchronous generator. Q is a point on the zpf
characteristics at 1.0 p.u voltage. The vertical
distance PO in figure gives the voltage drop across
The following Table gives four sets of staternens
as regards poles and torque. Select the corec
set corresponding to the mmf axis as shown
figure.
Torque
Surface
Stator Stator Rotor
Surface Surface Surface
ABC forms CDA forms abc forms
North Pole South Pole North Pole
South Pole
North Pole
North Pole
Rotor
Surface
cda forms
South Pole
South Pole
(a)
Sint
10-YO
Clock
Count
Code
Court
Clockwise
Clockwise
10) North Pole South Pole
South Polo
North Pole
d) South Pole
North Pole
South Pole
North Polo
Field current
Synchronous reactance
(b) Magnetizing reactance
(C) Potier reactance
Leakage reactance
[2003 : 1 Mark]
4.28 A4-pole, 3-phase, double-layer winding is housed
in a 36-slot stator for an ac machine with 80° phase
spread. Coil span is 7 short pitched. Number of
slots in which top and bottom layers belong to
different phases is
(b) 18
(c) 12
(d) 0
(2003 : 2 Marks)
4.29 When Stator and Rotor windings of a 2-pole
on the rotating electrical machine are excited, each would
produce a sinusoidal mmf distribution in the airgap
with peak values F, and F, respectively
[2003 : 2 Marks]
4.30 Two 3-phase, Y-connected alternators are to bi
paralleled to a set of common busbars. The
armature has a per phase synchronous reactance
of 1.7 and negligible armature resistance. The
line voltage of the first machine is adjusted to
3300 V and that of the second machine is adjusted
to 3200 V. The machine voltages are in phase
the instant they are paralleled. Under this condition
the synchronizing current per phase will be
(a) 16.98 A
(b) 29.41 A
(c) 33.96 A
(d) 58.82 A
(2004 : 2 Marks!
24 ??
4.31 A hydraulic turbine having rated speed of 250 rpm
is connected to a synchronous generator in order
to produce power at 50 Hz, the number of poles
required in the generator are
(a) 6
(b) 12
(c) 16
(d)/24
[2004 : 2 Marks)


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